Technical Abstract: Water use efficiency is a term often applied to irrigated conditions to determine the amount of applied water that is used by crops. Water use in irrigated watersheds can be managed by adjusting irrigation diversions to meet irrigation needs. Precipitation is often the only source of water input in many watersheds, and its rate and timing cannot be controlled. Excess water is often drained from the watershed through surface or subsurface drains to provide suitable conditions for crop growth. The objective of this paper is to compare water balances for the irrigated Upper Snake-Rock (USR) watershed in southern Idaho and the subsurface drained Upper Big Walnut Creek (UBWC) watershed in central Ohio. Irrigation water diverted from the Snake River supplied 80% of the water input into the USR watershed. Precipitation only supplied 10 to 20% of the water in the USR compared to 100% in the UBWC watershed. Potential crop ET was estimated to use 37 to 51% of the total annual water input in the USR watershed and 30 to 55% in the UBWC watershed. The relative volume of water potentially used by crops in these two watersheds was quite similar on an annual basis even though the hydrology throughout the year is quite different.